An ongoing 17 year follow-up study of 120,000 U.S. nurses has produced important information on causes and preventives of cancer and cardiovascular disease in white women (some 100 papers to date), and other large follow-up studies of white women have been started more recently. There are no comparable studies in black women, who bear a greater burden of illness and mortality. [Results on the etiology of disease in white women may not be generalizable to black women because of genetic differences, differences in risk factors, or other reasons.] We propose to conduct a large prospective follow-up study of black women to provide informative data on risk factors for cancer, cardiovascular disease, and other major illnesses, with an emphasis on the health effects of obesity. Other factors to be assessed include cigarette smoking, physical activity, alcohol use, die, exogenous estrogen use, and reproductive factors. We will enroll, by means of a mailed questionnaire, 50,000 black women up to age 69 years who are members of the National Education Association, employees of the federal government, nurses, or friends of these women. These women were chosen because of evidence that they can provide reliable health information and be followed with few losses. Pilot studies carried out with the assistance of both the National Education Association and the U.S. Office of Personnel Management have demonstrated the feasibility of the project. An Advisory Board of black women knowledgeable about health problems in the black community has participated and will continue to give advice and guidance; expert consultants on black women's health will have important input to the study. The initial questionnaire will collect information on exposures and covariates of interest. Follow-up mail questionnaires at 2-year intervals will update information and ascertain incident cases of cancer, cardiovascular disease, and other major illnesses; diagnoses will be documented by review of medical records and other documents. Deaths will be ascertained from families and friends and through the National Death Index. Interim mailings will be made to sustain the interest of the participants and to inform them of study results. This study will provide needed information on the etiology of disease in black women, a heretofore neglected group in health studies. [The etiologic results will generally be applicable to millions of U.S. black women, including poor women,] and the results will be useful in preventive programs focused on reducing morbidity and mortality.